It is the purpose of this proposal (1) to identify and characterize the inorganic mineral phase of bone, calcified cartilage, enamel, dentin, calcifying turkey tendon, and other mineralizing tissues, (2) to follow the time course changes in the chemical and structural nature of the mineral phase from its initial deposition to its most mature state in the respective tissues, and (3) to elaborate the sequence of progressively increasing degrees of mineralization and maturation with respect to the position, location, and orientation of the mineral phase deposits within structural elements, organelles, and compartments in osteogenic cells and extracellular tissue spaces. The major physical methods of investigation will be transmission and scanning electron microscopy, electron diffraction, and high spatial electron probe microanalysis, utilizing techniques for specimen preparation which will include both conventional, aqueous methods and anhydrous procedures we have previously developed employing organic solvents or dry ultracryomicrotomy.